1. Field of the Invention
The present invention is directed to a photocopy prevention method and, more particularly, to a photocopy prevention film comprising a volumetric holographic refraction grating fixed to a document along with the apparatus and method for producing a film.
2. Description of the Related Art
The unauthorized copying of classified or confidential documents ia a contemporary problem confronting many government agencies and corporations. FIG. 1 illustrates in general the key elements of a photocopy machine. A lamp 10 broadcasts diffused light onto a document 12 which scatters the light in many different directions. Some of the light is captured by lens 14 and focused onto a photoreceptor drum 16. As illustrated in FIG. 1, much of the light reflected from the document bypasses the lens 14, and as a result, the lamp 10 must produce a very large light flux in order for the lens 14 to capture sufficient light to activate the photoreceptor drum 16. The photocopy machines generally image with a small field angle in the direction of scan and a large semi-field angle of up to 35 degrees in the cross scan direction. The prior art methods of preventing photocopying include special colored papers and overlay materials that mask the original from casual duplication. One such method in which specular aluminum powder is deposited on the document is described in U.S. Pat. No. 4,066,280 to LaCaprica. Unfortunately, the original documents having the prior art copy prevention materials attached thereto suffer from a lack of contrast, making them difficult to read.